I never took it so literally, sure he was flying faster than normal to go around the earth, whereas the kryptonite weakened him so he couldn't do it originally as davejames suggested. However, I do not think that he was literally flying fast enough to cause the earth to spin the other way. This was merely an illustration for the audiences benefit.
See, when Jor-el told him not to interfere with human history, he wasn't referring to simply flying around and performing parlour tricks (this si supported by Supes revisit to the FOS in the extended cut) but that he should not tamper with time. There are hints in the film sprinkled throughout that the Kryptonians have some m,easure of control and mastery over time itself, and that is what makes them superior to Earthings . After all in his space capsule, Supes amassed a lot of informaiton from 12 galaxies in very little time. When he was in his twenties and in the FOS, he leaned a great deal more than 12 years would allow. When supes is flying around the world, you can see his struggle to access a power that had remained trather dormant, the ability to affect time. It was always there, and it took his rage at Lois' death to access that power.
That's my interpretation.
I've never believed that he reversed the rotation of the earth. Such an "concept" is a bit silly. As doing so would a)not likely reverse time b)be very disasterous to every. Single. Object. On the planet!
It was just a prespective thing to illustrated what it was he was doing. However, we *DO* see him flying very, very fast, infact he'd have to be flying faster than the Speed of Light to go backwards in time!
Now, sure all of that pent up rage and emotion drove him to go that fast, but still he has to know (per his "training" with Jor-El) he can fly, very, very fast. Certainly fast enough to catch up to two missiles. Flying to either side of the country or not. And ONE of the missiles was closeby in New Jersey (if we assume Metropolis in this movie is a New York stand-in). So he easily could've gotten both missiles without any effort and he was further a tool to fall for the "Detonator in the Box" trick Lex pulled on him.
All said. Superman 1 is still an awesome movie.